The present invention relates to the field of spinal correction devices. More specifically, the present invention is directed to a double barrel spinal fixation system and method that allow an operating surgeon to construct a rigid laminal claw across one or more vertebrae and provide subsequent independent reduction and fixation of a spinal deformity.
The use of spinal fixation systems is known. Such systems are used to correct spinal deformities such as: kyphosis, lordosis, hemivertebra, spondylolisthesis, scoliosis and others. Kyphosis is a sharp, angular rearward curvature. Lordosis is a forward accentuation of the cervical or lumbar regions beyond physiological levels. Hemivertebra is a developmental error in the spine caused by lack of formation of a vertebral body growth center which results in the production of wedge-shaped vertebrae or one-half of a vertebra. Spondylolisthesis is a spinal deformity in which a vertebral body with the vertebral column above it subluxes or glides forward on the vertebral body below. Scoliosis is characterized by a lateral curvature of a segment of the spine from the normally straight midline position. Other causes of spinal deformities include, but are not limited to, fractured vertrebral bodies or dislocated spinal segments. Spinal fixation systems are also used to correct spinal instability. Primary instability may be acute, for example, as caused by trauma; or may be chronic, for example, as caused by degeneration or by a tumor. Secondary instability may be caused by resection, for example, by a facetectomy. Secondary instability may also be caused by overload, for example, by a misalignment or from stress concentrations.
Many existing spinal fixation systems include rod and hook components used for reduction and fixation of the spinal column. However, the existing systems require the assembly of many different intricate components that ultimately cause the surgical procedure to be complicated and unnecessarily delayed.
For example, U.S. Pat. No. 5,102,412 to Rogozinski shows a spinal rod system and method for instrumenting the spine in the treatment of spinal abnormalities. The system comprises many intricate parts. Such parts include U-shaped screw couplers for use with pedicular screws. The screw couplers are assembled with cross bars and set screws. The laminar clawing configuration requires the additional assembly of a hook bar and a set screw. Another example of spinal instrumentation is known as the Multiple Axial Stabilization System (MASS). This system uses open hooks and cable hooks. Clawing of lamina is accomplished by interconnecting either cable hooks with open hooks, or by interconnecting a pair of cable hooks. A longitudinal rod can subsequently be inserted into the groove in the open slot outside of the open hook. Provided absolute alignment with the groove is established, a sleeve can be positioned outside the rod and integral with the open hook to secure the hook to the rod. It has been found in practice that it is often cumbersome to align the rod with the groove in the clamp. The improper alignment between the rod and the groove can cause the insertion of the sleeve into the hook to be difficult. In addition, the cabling system is not sufficiently rigid to provide rotational stability.
The Isola spinal implant system is a further example of spinal instrumentation and is described in Spinal Instrumentation, pp. 324-351 (1992). The Isola system uses anchor components consisting of screws, posts, hooks and wires. Closed body and open body hooks are used. The anchors, and in particular, the hooks, are used to interconnect longitudinal rods to achieve the desired correction of spinal deformity about the sagittal plane. The hooks are placed in operative association with selected lamina while simultaneously interconnecting the longitudinal rod members.
Similarly, the Correl-Dubousset Instrumentation includes closed and open hook bodies. The hooks are used as anchor points to interconnect a flexible rod. A closed body hook and an open body hook may be used to span one or more lamina but such an installation is still integral to the total longitudinal rod component and does not allow an independent clawing of the selected lamina.
It is desirable to have a device that will allow an operating surgeon to construct a rigid laminal clamp that is independent of the rod system. The device should allow the surgeon to be able to concentrate upon the task of clawing one or multiple lamina without having to simultaneously coordinate the installation of the rod system. The device should also be easy to assemble and should provide torsional stability to correct rotational deformity of the spine. The device should be adaptable for use with pedicular bolts and with laminar hooks. The device should also be easy to install by allowing the surgeon to readily insert the longitudinal rod into the slot of the clamp and thereafter to secure the longitudinal rod when it is in the correct position.